Sunset defined: Where the glow comes from and how it looks so good

Weather Glossary

In this Thursday, April 2, 2020 photo, an oil rig lights up the horizon on the outskirts of Midland, Texas after a late sunset. (Odessa American/Eli Hartman)

ROCHESTER, NY (WROC) – Let’s focus on the sunrise and sunset for this purpose. Basically whenever the sun is close to the horizon. The sun is where we’ll start. The sun emits many different wavelengths of radiation. The two we think about are UV and color. UV is the one that can give us a sunburn and color is the one that illuminates everything so we can see.

Note that visible light is just a small sliver of the entire solar spectrum.

Many of these wavelengths get absorbed by the atmosphere. Focusing on visible light, the entire spectrum of visible light makes it to our eyes when the sun is high in the sky. When you put them all together, you get white light. While no one should be looking at the sun, you can trust me here that it is white light, not yellow. Note below the wavelength of each light. As certain wavelengths hit your eye, those are the ones that were not scattered away by atmospheric particles. The shorter the wavelength, the more energy it has. The longer the wavelength, the less energy it has.

Since the color blue is a shorter wavelength, it is the one that is able to make it to your eye. The longer wavelengths are scattered away from your eye. This is why the sky is blue when there are no clouds and the sun is high in the sky. Clouds are white because they absorb all the colors and reflect them into your eye. When clouds scatter light, it is called Mie Scattering.

The scattering that occurs in the atmosphere is called Rayleigh Scattering, named after Lord Rayleigh. That is when the light runs into the gasses within the atmosphere (nitrogen, oxygen, etc). These gases are smaller than the particles of light, so scattering of the light occurs.

Image courtesy: NOAA


Note that in the spectrum above, longer wavelengths consist of yellow, orange, red, and deep red. During twilight (the time before/after the sunrise/sunset when light is emerging/declining) the light of the sun is traveling through a thicker layer of the atmosphere and most of the light is being scattered away from your eye. The longer wavelengths are the only ones that actually make it to your eye. During completely clear skies if you look hard enough, you can see the entire spectrum of light. The best sunrise/sunsets occur with some clouds involved.

Below shows three examples of light. (A) shows light that would be blue as that is the dominant light. According to NOAA: “Blue light waves scatter at a rate about four times stronger than red light waves. The volume of scattering by the shorter blue light waves (with additional scattering by violet and indigo) dominate scattering by the remaining color wavelengths. Therefore, we perceive the blue color of the sky.

(B) is when more atmosphere is involved in the travel of light particles, allowing for longer wavelenths to reach your eye. The first up would be yellow. (C) is showing how as the sun nears the horizon, the longest wavelengths of light will reach your eye and the sky will turn those colors.

Image courtesy: NOAA

A bonus for photographing sunsets is using bodies of water to your advantage. Reflection can really spice up a sunrise or sunset.

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